1. Field of the Invention
This invention is related to an apparatus for analysing an individual's speech and more particularly, to an apparatus for analysing pitch perturbations to determine the individual emotional state such as stress, depression, anxiety, fear, happiness, etc., which can be indicative of subjective attitudes, character, mental state, physical state, gross behavioral patterns, veracity, etc. In this regard, the apparatus has commercial applications as a criminal investigative tool, a medical and/or psychiatric diagnostic aid, a public opinion polling aid, etc.
2. Description of the Prior Art
One type of technique for speech analysis to determine emotional stress is disclosed in Bell Jr., et al., U.S. Pat. No. 3,971,034. In the technique disclosed in this patent a speech signal is processed to produce an FM demodulated speech signal. This FM demodulated signal is recorded on a chart recorder and then is manually analysed by an operator. This technique has several disadvantages. First, the output is not a real time analysis of the speech signal. Another disadvantage is that the operator must be very highly trained in order to perform a manual analysis of the FM demodulated speech signal and the analysis is a very time consuming endeavor. Still another disadvantage of the technique disclosed in Bell Jr., et al. is that it operates on the fundamental frequencies of the vocal cords and, in the Bell Jr., et al. technique tedious re-recording and special time expansion of the voice signal are required. In practice, all these factors result in an unnecessarily low sensitivity to the parameter of interest, specifically stress.
Another technique for voice analysing to determine emotional states is disclosed in Fuller, U.S. Pat. Nos. 3,855,416, 3,855,417, and 3,855,418. The technique disclosed in the Fuller patents analyses amplitude characteristics of a speech signal and operates on distortion products of the fundamental frequency commonly called vibrato and on proportional relationships between various harmonic overtone or higher order formant frequencies.
Although this technique appears to operate in real time, in practice, each voice sample must be calibrated or normalized against each individual for reliable results. Analysis is also limited to the occurrence of stress, and other characteristics of an individual's emotional state cannot be detected.